Vibration damping devices designed for installation between components making up a vibration transmission system, such as the power unit and the vehicle body of an automobile, in order to provide vibration-damped coupling and vibration-damped support between the components, are known in the art. Such vibration damping devices have a construction whereby a first mounting fitting attached to one component of the vibration transmission system and a second mounting fitting attached to the other component of the vibration transmission system are elastically linked by a main rubber elastic body. Fluid-filled type vibration damping devices, which utilize the flow action of a noncompressible fluid filling the interior, have been proposed as one class of vibration damping device. A typical fluid-filled type vibration damping device has a construction that includes a pressure-receiving chamber whose wall is partially constituted by the main rubber elastic body and an equilibrium chamber whose wall is partially constituted by a flexible film, with the pressure-receiving chamber and the equilibrium chamber communicating with one another through an orifice passage.
One problem encountered with fluid-filled type vibration damping devices is that whereas vibration damping action based on resonance action of the fluid is excellent for vibration at frequencies to which the orifice passage has been pre-tuned, it is difficult to achieve effective vibration damping action against vibration at frequencies lying outside the tuning frequency of the orifice passage. In particular, at times of input of vibration of higher frequency range than the tuning frequency of the orifice passage, the orifice passage becomes substantially blocked due to antiresonance action, creating a problem of markedly degraded vibration damping capabilities resulting from a high dynamic spring rate.
With the aim of achieving reductions in dynamic spring arising at times of input of vibration of a high frequency range, there has been proposed a fluid-filled type vibration damping device that features arranging a moveable plate on a partition member separating the pressure-receiving chamber from the equilibrium chamber, to provide a fluid pressure-absorbing mechanism that utilizes minute displacement of the moveable plate. The vibration damping device is designed to accommodate the moveable plate arranged so as to be capable of minute displacement with respect to a housing (partition member), with pressure of the pressure-receiving chamber exerted on one face of the moveable plate, while pressure of the equilibrium chamber is exerted on the other face. At times of vibration input, the moveable plate experiences minute displacement along the direction of plate thickness due to relative pressure fluctuations between the pressure-receiving chamber and the equilibrium chamber, so that liquid pressure of the pressure-receiving chamber is dispelled into the equilibrium chamber, attaining a low dynamic spring rate in the pressure-receiving chamber. One such fluid-filled type vibration damping device is that disclosed in Patent Citation 1 for example.
However, the fluid-filled type vibration damping device disclosed in Patent Citation 1 has the problem that because the moveable plate is accommodated in a rigid housing (partition member), minute displacement of the moveable plate along its thickness direction gives rise to noise caused by striking against the partition member. Striking noise of the moveable plate is a particular problem in Patent Citation 1, because the moveable plate is arranged across a gap lying in the direction of plate thickness with respect to the housing.